Bandit

Bandit is an HTTP server for Plug and WebSock apps.

Bandit is written entirely in Elixir and is built atop Thousand Island. It can serve HTTP/1.x, HTTP/2 and WebSocket clients over both HTTP and HTTPS. It is written with correctness, clarity & performance as fundamental goals.

In ongoing automated performance tests, Bandit’s HTTP/1.x engine is up to 4x faster than Cowboy depending on the number of concurrent requests. When comparing HTTP/2 performance, Bandit is up to 1.5x faster than Cowboy. This is possible because Bandit has been built from the ground up for use with Plug applications; this focus pays dividends in both performance and also in the approachability of the code base.

Bandit also emphasizes correctness. Its HTTP/2 implementation scores 100% on the h2spec suite in strict mode, and its WebSocket implementation scores 100% on the Autobahn test suite, both of which run as part of Bandit’s comprehensive CI suite. Extensive unit test, credo, dialyzer, and performance regression test coverage round out a test suite that ensures that Bandit is and will remain a platform you can count on.

Lastly, Bandit exists to demystify the lower layers of infrastructure code. In a world where The New Thing is nearly always adding abstraction on top of abstraction, it’s important to have foundational work that is approachable & understandable by users above it in the stack.

Project Goals

• Implement comprehensive support for HTTP/1.0 through HTTP/2 & WebSockets (and beyond) backed by obsessive RFC literacy and automated conformance testing
• Aim for minimal internal policy and HTTP-level configuration. Delegate to Plug & WebSock as much as possible, and only interpret requests to the extent necessary to safely manage a connection & fulfill the requirements of safely supporting protocol correctness
• Prioritize (in order): correctness, clarity, performance. Seek to remove the mystery of infrastructure code by being approachable and easy to understand
• Along with our companion library Thousand Island, become the go-to HTTP & low-level networking stack of choice for the Elixir community by being reliable, efficient, and approachable

Project Status

• Complete support for Phoenix applications (WebSocket support requires Phoenix 1.7+)
• Complete support of the Plug API
• Complete support of the WebSock API
• Complete server support for HTTP/1.x as defined in RFC 9112 & RFC 9110
• Complete server support for HTTP/2 as defined in RFC 9113 & RFC 9110, comprehensively covered by automated h2spec conformance testing
• Complete server support for WebSockets as defined in RFC 6455, comprehensively covered by automated Autobahn conformance testing. Per-message compression as defined in RFC 7692 is also supported
• Extremely scalable and performant client handling at a rate up to 4x that of Cowboy for the same workload with as-good-or-better memory use

Any Phoenix or Plug app should work with Bandit as a drop-in replacement for Cowboy; exceptions to this are errors (if you find one, please file an issue!).

Using Bandit With Phoenix

Bandit fully supports Phoenix. Phoenix applications which use WebSockets for features such as Channels or LiveView require Phoenix 1.7 or later.

Using Bandit to host your Phoenix application couldn’t be simpler:

1. Add Bandit as a dependency in your Phoenix application’s mix.exs:

    {:bandit, ">= 0.7.1"}

2. Add the following to your endpoint configuration in config/config.exs:

     config :your_app, YourAppWeb.Endpoint,
       adapter: Bandit.PhoenixAdapter

3. That’s it! You should now see messages at startup indicating that Phoenix is using Bandit to serve your endpoint.

For more details about how to configure Bandit within Phoenix, consult the Bandit.PhoenixAdapter documentation.

Using Bandit With Plug Applications

Using Bandit to host your own Plug is very straightforward. Assuming you have a Plug module implemented already, you can host it within Bandit by adding something similar to the following to your application’s Application.start/2 function:

def start(_type, _args) do
  children = [
    {Bandit, plug: MyApp.MyPlug}
  ]

  opts = [strategy: :one_for_one, name: MyApp.Supervisor]
  Supervisor.start_link(children, opts)
end

Bandit takes a number of options at startup, which are described in detail in the Bandit documentation.

For less formal usage, you can also start Bandit using the same configuration options via the Bandit.start_link/1 function:

# Start an http server on the default port 4000, serving MyApp.MyPlug
Bandit.start_link(plug: MyPlug)

WebSocket Support

If you’re using Bandit to run a Phoenix application as suggested above, there is nothing more for you to do; WebSocket support will ‘just work’.

If you wish to interact with WebSockets at a more fundamental level, the WebSock and WebSockAdapter libraries provides a generic abstraction for WebSockets (very similar to how Plug is a generic abstraction on top of HTTP). Bandit fully supports all aspects of these libraries.

Implementation Details

Bandit’s HTTP/2 implementation is described in detail in its own README. Similar documentation for the HTTP/1.x and WebSocket implementations is a work in progress.

Contributing

Contributions to Bandit are very much welcome! Before undertaking any substantial work, please open an issue on the project to discuss ideas and planned approaches so we can ensure we keep progress moving in the same direction.

All contributors must agree and adhere to the project’s Code of Conduct.

Security disclosures should be handled per Bandit’s published security policy.

Installation

Bandit is available in Hex. The package can be installed by adding bandit to your list of dependencies in mix.exs:

def deps do
  [
    {:bandit, ">= 0.7.1"}
  ]
end

Documentation can be found at https://hexdocs.pm/bandit.

License

MIT